sound-theme-freedesktop: Fix license format QA error

Fix the following QA error:

,----
| WARNING: Recipe sound-theme-freedesktop, LICENSE (GPLv2+ CC-BY-3.0
|     CC-BY-SA-3.0) has invalid format, LICENSES must have operator "([&|()
|     ])" between them.
`----

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>